The present invention relates to a color image forming method and device for forming a color image on a recording medium by processing input color image data and, more particularly, to a method and device for recording a specific information on an output image adding to a color image on a recording medium a specific pattern that is unrecognizable by human eyes and recognizable by recognizing means.
The recent development of image forming devices in respect to forming an image being true to an original image has created the possibility of reproducing, by using color image forming device such as color copiers in particular, faithful color copies that are true to and cannot be distinguished by human eye from the original. This arises a problem of reproduction of faithful color copies of prohibited originals by using color image forming devices including color copiers.
To prevent the reproduction of the prohibited originals, two kinds of techniques have been applied to image forming devices. The first technique forces a color forming device to extract a feature of an input original image, which indicates the prohibition on its illegal reproduction, and causes the device to further reproduce such the prohibited material. The second technique causes the device to apply specific additional information to an image formed from an input original in order to clearly indicate that the formed image is a copy of the copyrighted original.
The second technique has the following two examples:
Japanese Patent Publication No. 2614369 describes a technique for attaching a specific pattern onto a color image by using coloring materials difficult to be recognized by human eyes (for example, a yellow color pattern on a recording medium such as white recording paper) when outputting the color image according to data of an input color image using a plurality of visible coloring materials.
This method characterized by putting a specific pattern unique to the device by using coloring material difficult to be recognized by human eyes. Therefore, it not only prevents the natural color effect of a copy product from being changed but also surely identify the image forming device by which the product was produced by the pattern added thereto.
Japanese Laid-Open Patent Publication No. 6-62217 describes a technique by which additional information (a pattern of symbols) being absent on an original image is modulated in accord with the intensity of an image signal input from an original material and then put on an output image to be reproduced by an image forming device. Namely, the symbol pattern intensity is weakened for a highlight portion of the image where human eyes have sharp sensitivity to a difference in optical density, while it is enhanced for a shadow portion where human eyes have low sensitivity to a difference in optical density.
This method can surely read a symbol pattern in any range of optical densities, making at the same time the symbol pattern be quiet.
The above-mentioned techniques, however, have the following respective problems.
A problem involved in the first technique is such that an allowable image cannot be reproduced or a prohibited image is reproduced if an original image is misjudged.
The second technique may be free from the trouble of the first technique but may have a decrease in image quality of a copy product since additional information is added to an original image.
Concerning the above drawback of the second technique, the methods disclosed in Japanese Patent Publication No. 2614369 and Japanese Laid-Open Patent Publication No. 6-62217 devise adding a specific pattern or a symbol pattern in such a manner that a decrease in quality of a copied image may be minimized. However, both methods still involve the following problems:
The method disclosed in Japanese Patent Publication No. 2614369 applies a specific pattern with coloring material (yellow) difficult to be recognized by human eyes. However, such the yellow pattern is striking in respect to other image portion having a particular color (e.g., blue).
The method disclosed in Japanese Laid-Open Patent Publication No. 6-62217 may have a striking symbol pattern (specific pattern) in a shadow portion (of high optical density) due to the enhancement of the pattern intensity.
In view of the above circumstances, the present invention was made with a primary object to provide an image forming device and method, which can obtain an output image combined (synthesized) from a specific pattern and a processed input image with no decrease in quality of an output image and which is featured by adding the specific pattern with a color that is unrecognizable by human eyes but recognizable by a recognizing device.
To achieve the above-described purpose, the present invention provides the following technical means:
A first technical means of the present invention is a color image forming device that comprises an image inputting means for inputting color image data, an image processing means for generating output color image data by processing the input image data according to a predetermined procedure, an image forming means for forming a color image on a recording medium by using of a plurality of visible coloring materials based on the output color image data, a specific pattern generating means for generating a specific pattern indicating specified information and a color-data adding means for adding data of the specific pattern to the output color image data so as to attach the specific pattern, wherein the color-data adding means adds the specific pattern data to the output color image data in such a manner that the specific pattern formed on the color image is hardly recognizable by human eyes but recognizable by a recognizing means.
In the above arrangement of the technical means, the color data adding means can provide an output image with a specific pattern which is difficult to be distinguished (recognized) by human vision but can surely be recognized by a recognizing means. Is proposed a method that utilizes a uniform color space of the L*a*b* color system defined by CIE (Commission Internationale de l""Eclairage), which system has a spectral sensitivity characteristic closest to the sensitivity of human eyes. Since the sensitivity characteristic of a charge coupled device (CCD) built in a recognizing means such as a color scanner is based on the common RGB color system, a specific pattern is added to an output color image data by using a color that has a small difference in the L*a*b* color system but can surely be recognized as a RGB color signal by the CCD. The specific pattern is thus added in the manner not to be distinguished by human eyes, so it does not impair the output image quality and can surely identify, by the specific pattern added to the color copy product, the color image device by which the product was produced.
A second technical means of the present invention has the same construction as that of the first technical means, wherein the color-data adding means adds a specific pattern data to the output color image data so that the specific pattern is formed on the output color image by using a color having a minimum color difference for the formed color image.
In addition to the effect of the first technical means, the second technical means enables the color data adding means to form the specific pattern not to be distinguished by human eyes from any other colored area in a range from low optical density to a high optical density owing to use of the color of the specific pattern, which has a minimum difference from a color of a surrounding area. This method is based on the fact that human""s sense of sight cannot distinguish a small difference between two colors.
A third technical means of the present invention has the same construction as that of the first or second technical means, wherein the color-data adding means includes a memory means for storing a predetermined relation between the input color image data and output color image data and calculates a color of the specific pattern based on the input color image and the relation stored in the memory means.
In addition to the effect of the first or second technical means, the third technical means keeps in a memory data on the predetermined relation between input color image data and output color image data, so it can immediately select with ease an optimal color for the specific pattern to be added to the output image data. An exemplified relation between the input color image data and the output color image data is defined as a relation between color image data (RGB) read by an image inputting means and a uniform color space of the L*a*b* color system and a relation between the uniform color space and an output (YMCK) of an image output unit. Both relations are determined respectively by using a suitable method such as a neutral network and a method for determining coefficients for mask operation. The optimal color can thus determined based on the calculated relations.
A fourth technical means of the present invention has the same construction as that of the first or the second technical means, wherein the color-data adding means includes a color-data calculating means for determining the specific pattern color based on the input color image data.
In addition to the effect of the first or the second technical means, the fourth technical means can determine an optimal color of the specific pattern by calculation based on the input color image data with no need for additional memory capacity.
A fifth technical means of the present invention has the same construction as that of any of the first to fourth technical means, wherein the color-data adding means includes a combining means for combining the specific pattern data with the output color image data obtained from the image processing means.
In addition to the effect of any of the first to fourth technical means, the fifth technical means is provided with the combining (synthesizing) means for the color data adding means and can easily combine a specific pattern data with output color image data obtained by the image processing means. The image processing means processes input color image data read by the image inputting means, while the color adding means generates a specific pattern with a color that is hardly recognizable by human eyes but recognizable by a recognizing means. The processed color image data and the specific pattern data can be easily combined into output color image data by the combining means of the color adding means.
A sixth technical means of the present invention has the same construction as that of any one of the first to fourth technical means, wherein the color image processing means includes a combining portion for combining the specific pattern data from the color-data adding means with the input color image data to generate output color image data including the specific pattern data.
In addition to the effect of any of the first to fourth technical means, the sixth technical means is provided with the combining portion for the image processing means and can previously combine specific pattern color data with color image data to be output to the image forming means. The image processing means can thus generate output color image data including specific pattern data.
A seventh technical means of the present invention comprises an image processing step for generating output color image data by processing color image data according to a predetermined procedure, an image forming step for forming a color image on a recording medium by using a plurality of visible coloring materials, a color-data adding step for attaching a specific pattern indicating specific information to the color image by adding data of the specific pattern to the output color image data, wherein the specific pattern data is that the specific pattern formed on the color image is hardly recognizable by human eyes but recognizable by a recognizing means.
The above-described method can provide an output color image data with specific pattern that is difficult to be distinguished by human eyes but can be recognized by the recognizing means. In practice, an example is a method using a uniform color space of the CIE color system L*a*b* having a sensitivity characteristic closest to that of human eyes. In view of the fact that a charge coupled device (CCD) of a recognizing means such as a scanner has a sensitivity characteristic based on the usual RGB color system, a specific pattern is added to an output color image by using a color that has a small difference from the output image color according to the L*a*b* color system but can be clearly distinguished according to the RGB color system. Since the specific pattern added to the output color image is difficult to be distinguished by human eyes, the output color image may not be suffered to impairment of its quality and may surely identify, by the specific pattern added thereto, the image-forming device by which it was reproduced from the original.
An eighth technical means of the present invention has the same construction as that of the seventh technical, wherein the color-data adding step adds the specific pattern data to the output color image data so that the specific pattern is formed on the output color image by using a color having a minimum color difference for the formed color image. In addition to the effect of the seventh technical means, the eighth technical means can form the specific pattern not to be distinguished by human eyes from any other colored area in a range from low optical density to a high optical density owing to use of the color of the specific pattern, which has a minimum difference from that of a surrounding area.
A ninth technical means of the present invention has the same construction as that of the seventh or eighth technical means, wherein the color-data adding step determines a color of the specific pattern based on the input color image data.
In addition to the effect of the seventh or eighth means, the ninth technical means has the color-data adding step which can determine an optimal color based on input color image data with no need for use any additional memory.
A tenth technical means of the present invention has the same construction as that of any one of the seventh to ninth technical means, wherein the color data adding step which is used for determining the specific pattern data, further comprises a first calculating step for calculating a relation between the input color image data and a uniform color space, a second calculating step for determining a minimum value of a color difference between the input color-image data and data variable within a given range of color image data to be inputted, a third calculating step for converting the minimum color-difference value into the output color image data and a fourth calculating step for determining a relation between output color image data and a uniform color space.
According to the tenth technical means, it is possible to obtain, in addition to the effect of any of the seventh to ninth technical means, an advantage of surely determining with ease a color of the specific pattern having a least color difference value, which can be attached to the output color image data and can be surely recognized on the output color image by recognizing means. It is also possible to previously determine the relation between various kinds of input color-image data and the uniform color space, which enables the recognizing means to surely recognize the specific pattern.
The color image forming device and the color image forming method according to the present invention will be described with reference to the following accompanying drawings.